1. Field of the Invention
The present invention relates, in general, to an image correction method for a camera system that can correct mounting errors of a camera caused when the camera is not accurately located in a desirable posture at a target location.
2. Description of the Related Art
In a camera system, in particular, a camera system which generates around views using one or more cameras, mounting error of the camera or cameras cause defects in around views, such as misalignments in images captured by the individual cameras.
In some vehicles, such a camera system is mounted to generate around views. One of the examples of the camera system is an Around View Monitor (AVM) system. Typically, the AVM system is tuned on the assumption that the cameras will be accurately arranged at planned locations and with planned postures (hereinafter simply referred to as “planned positions”). Such a tuning status does not retain its original quality after having passed along an actual mass production line of vehicles. This is due to mounting errors beyond tolerance that occur when the cameras are mounted on vehicles.
FIG. 1 illustrates an example of defects of an all-around view in an AVM system, due to the mounting errors of cameras. Such an AVM system generates an all-around view 6 including four images captured by four cameras mounted on the front, rear, left and right sides of a vehicle. Due to the mounting errors, optical axes of respective cameras deviate from their planned positions, thus resulting in misalignment sections 2 between the captured images of the cameras.
Many methods to eliminate the above-described defects have been proposed. One of the methods is to eliminate the defects on the basis of a software, as disclosed in U.S. Patent Application Publication No. 2009/0010630. This method is described briefly with reference to FIGS. 2 and 3.
As shown in FIG. 2, a vehicle 1, equipped with four cameras for an AVM system on the front, rear, left and right sides thereof in a vehicle mass production line, is located in a calibration area 3 in which four “+”-shaped ground marks 5 are drawn on a reference ground 4. The AVM system matches images captured by individual cameras with one another, and then outputs the images from the individual cameras or a combined all-around view 6 to the screen.
The four ground marks 5 are arranged at locations corresponding to those of the optical axes of the respective cameras when the four cameras are accurately mounted at planned positions. When, e.g., a front camera is moved from its planned position to the right and deviates clockwise due to mounting errors, the image captured by the front camera also deviates in the same way as that of the front camera, as shown in FIG. 3. In FIG. 3, a ground mark captured by the front camera, that is, a captured mark 7, is illustrated to be deviated to the right on the screen.
According to the above reference, the correction of defects attributable to the mounting errors of cameras is performed in such a way as to measure the horizontal error (ΔX), the vertical error (ΔY) and the rotational error (Δθ) of an optical axis, correct the vertical and horizontal errors of the optical axis, and correct the rotational error of the optical axis. Here, in particular, the correction of the rotational error is performed by selecting a map most suitable for the correction of the measured rotational error (Δθ) from a plurality of maps previously provided depending on various rotational errors of the optical axis.
This method, however, requires a number of maps corresponding to the number of various cases as described above. As a result, the amount of data which must be stored by the AVM system may be excessively large.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.